Fritz Vahrenholt, one of Germany's earliest green energy investors, is
not convinced that humanity is causing catastrophic global warming. He writes in UK Daily Telegraph:

"For many years, I was an active supporter of the IPCC and its CO2
theory. Recent experience with the UN's climate panel, however, forced
me to reassess my position. In February 2010, I was invited as a
reviewer for the IPCC report on renewable energy. I realised that the
drafting of the report was done in anything but a scientific manner. The
report was littered with errors and a member of Greenpeace edited the
final version. These developments shocked me. I thought, if such things
can happen in this report, then they might happen in other IPCC reports
too "